gpg: Add option --assert-pubkey_algo.

* g10/keyid.c (parse_one_algo_string): New.
(compare_pubkey_string_part): New.
(compare_pubkey_string): New.
* g10/verify.c (check_assert_signer_list): New.
* g10/mainproc.c (check_sig_and_print): Call check_assert_pubkey_algo.
* g10/options.h (opt): Add field assert_pubkey_algos.
* g10/gpg.c (oAssertPubkeyAlgo): New.
(opts): Add "--assert-pubkey_algo".
(assert_pubkey_algo_false): New.
(main): Parse option.
(g10_exit): Reorder RC modifications.  Check assert_pubkey_algo_false.
* common/status.h (ASSERT_PUBKEY_ALGOS): new.
* common/t-support.h (LEAN_T_SUPPORT): Use a simplified version if
this macro is set.

* g10/gpgv.c (oAssertPubkeyAlgo): New.
(opts): Add "--assert-pubkey_algo".
(assert_pubkey_algo_false): New.
(main): Parse option.
(g10_exit): Check assert_pubkey_algo_false.

* g10/t-keyid.c: New.
* g10/Makefile.am: Add t-keyid.
* g10/test-stubs.c: Add assert_pubkey_algos and assert_signer_list and
remove from other tests.
(check_assert_signer_list): Ditto.
(check_assert_pubkey_algo): Ditto.
--

GnuPG-bug-id: 6946

20 files changed, 425 insertions, 59 deletions

diff --git a/common/status.h b/common/status.h
index d249174d1..0a1266d3c 100644
--- a/common/status.h
+++ b/common/status.h
@@ -54,6 +54,7 @@ enum
     STATUS_NEED_PASSPHRASE,
     STATUS_VALIDSIG,
     STATUS_ASSERT_SIGNER,
+    STATUS_ASSERT_PUBKEY_ALGO,
     STATUS_SIG_ID,
     STATUS_ENC_TO,
     STATUS_NODATA,
diff --git a/common/t-support.h b/common/t-support.h
index 7aa46c00c..aa1b560fc 100644
--- a/common/t-support.h
+++ b/common/t-support.h
@@ -31,6 +31,8 @@
 #ifndef GNUPG_COMMON_T_SUPPORT_H
 #define GNUPG_COMMON_T_SUPPORT_H 1
 
+#ifndef LEAN_T_SUPPORT
+
 #ifdef GCRYPT_VERSION
 #error The regression tests should not include with gcrypt.h
 #endif
@@ -45,11 +47,6 @@
 # define getenv(a)  (NULL)
 #endif
 
-#ifndef DIM
-# define DIM(v)		     (sizeof(v)/sizeof((v)[0]))
-# define DIMof(type,member)   DIM(((type *)0)->member)
-#endif
-
 
 /* Replacement prototypes. */
 void *gcry_xmalloc (size_t n);
@@ -65,6 +62,12 @@ void  gcry_free (void *a);
 #define xstrdup(a)    gcry_xstrdup ( (a) )
 #define xfree(a)      gcry_free ( (a) )
 
+#endif /* LEAN_T_SUPPORT */
+
+#ifndef DIM
+# define DIM(v)		     (sizeof(v)/sizeof((v)[0]))
+# define DIMof(type,member)   DIM(((type *)0)->member)
+#endif
 
 /* Macros to print the result of a test.  */
 #define pass()  do { ; } while(0)
diff --git a/doc/DETAILS b/doc/DETAILS
index fd95e511c..29e39708b 100644
--- a/doc/DETAILS
+++ b/doc/DETAILS
@@ -527,6 +527,12 @@ pkd:0:1024:B665B1435F4C2 .... FF26ABB:
     --assert-signer is used.  The fingerprint is printed with
     uppercase hex digits.
 
+*** ASSERT_PUBKEY_ALGO <fingerprint> <state> <algostr>
+    This is emitted when option --assert-pubkey-algo is used and the
+    signing algorithms is accepted according to that list if state is
+    1 or denied if state is 0.  The fingerprint is printed with
+    uppercase hex digits.
+
 *** SIG_ID  <radix64_string>  <sig_creation_date>  <sig-timestamp>
     This is emitted only for signatures of class 0 or 1 which have
     been verified okay.  The string is a signature id and may be used
diff --git a/doc/gpg.texi b/doc/gpg.texi
index 2f5b613d8..26e0ebdcd 100644
--- a/doc/gpg.texi
+++ b/doc/gpg.texi
@@ -1917,6 +1917,29 @@ is guaranteed to return with an exit code of 0 if and only if a
 signature has been encountered, is valid, and the key matches one of
 the fingerprints given by this option.
 
+@item --assert-pubkey-algo @var{algolist}
+@opindex assert-pubkey-algo
+During data signature verification this options checks whether the
+used public key algorithm matches the algorithms given by
+@var{algolist}.  This option can be given multiple times to
+concatenate more algorithms to the list; the delimiter of the list are
+either commas or spaces.
+
+The algorithm names given in the list may either be verbatim names
+like "ed25519" with an optional leading single equal sign, or being
+prefixed with ">", ">=", "<=", or "<".  That prefix operator is
+applied to the number part of the algorithm name; for example 2048 in
+"rsa2048" or 384 in "brainpoolP384r1".  If the the leading non-digits
+in the name matches, the prefix operator is used to compare the number
+part, a trailing suffix is ignored in this case.  For example an
+algorithm list ">rsa3000, >=brainpool384r1, =ed25519" allows RSA
+signatures with more that 3000 bits, Brainpool curves 384 and 512,
+and the ed25519 algorithm.
+
+With this option gpg (and also gpgv) is guaranteed to return with an
+exit code of 0 if and only if all valid signatures on data are made
+using a matching algorithm from the given list.
+
 
 @item --auto-key-locate @var{mechanisms}
 @itemx --no-auto-key-locate
diff --git a/doc/gpgv.texi b/doc/gpgv.texi
index 2dd9576b6..54ab23383 100644
--- a/doc/gpgv.texi
+++ b/doc/gpgv.texi
@@ -140,6 +140,10 @@ This option enables a mode in which filenames of the form
 @file{-&n}, where n is a non-negative decimal number,
 refer to the file descriptor n and not to a file with that name.
 
+@item --assert-pubkey-algo @var{algolist}
+@opindex assert-pubkey-algo
+This option works in the same way as described for @command{gpg}.
+
 @end table
 
 @mansect return value
@@ -190,4 +194,3 @@ The default keyring with the allowed keys.
 @mansect see also
 @command{gpg}(1)
 @include see-also-note.texi
-
diff --git a/g10/Makefile.am b/g10/Makefile.am
index c5691f551..e8d8e9017 100644
--- a/g10/Makefile.am
+++ b/g10/Makefile.am
@@ -183,7 +183,7 @@ gpgv_LDFLAGS =
 
 
 t_common_ldadd =
-module_tests = t-rmd160 t-keydb t-keydb-get-keyblock t-stutter
+module_tests = t-rmd160 t-keydb t-keydb-get-keyblock t-stutter t-keyid
 t_rmd160_SOURCES = t-rmd160.c rmd160.c
 t_rmd160_LDADD = $(t_common_ldadd)
 t_keydb_SOURCES = t-keydb.c test-stubs.c $(common_source)
@@ -200,6 +200,10 @@ t_stutter_SOURCES = t-stutter.c test-stubs.c \
 t_stutter_LDADD = $(LDADD) $(LIBGCRYPT_LIBS) \
 	      $(LIBASSUAN_LIBS) $(NPTH_LIBS) $(GPG_ERROR_LIBS) $(NETLIBS) \
 	      $(LIBICONV) $(t_common_ldadd)
+t_keyid_SOURCES = t-keyid.c test-stubs.c $(common_source)
+t_keyid_LDADD = $(LDADD) $(LIBGCRYPT_LIBS) \
+              $(LIBASSUAN_LIBS) $(NPTH_LIBS) $(GPG_ERROR_LIBS) $(NETLIBS) \
+	      $(LIBICONV) $(t_common_ldadd)
 
 
 $(PROGRAMS): $(needed_libs) ../common/libgpgrl.a
diff --git a/g10/gpg.c b/g10/gpg.c
index d4fbecdbe..1d0b9d09e 100644
--- a/g10/gpg.c
+++ b/g10/gpg.c
@@ -451,6 +451,7 @@ enum cmd_and_opt_values
     oCompatibilityFlags,
     oAddDesigRevoker,
     oAssertSigner,
+    oAssertPubkeyAlgo,
     oKbxBufferSize,
 
     oNoop
@@ -715,6 +716,7 @@ static gpgrt_opt_t opts[] = {
 #endif
   ARGPARSE_s_s (oAddDesigRevoker, "add-desig-revoker", "@"),
   ARGPARSE_s_s (oAssertSigner,    "assert-signer", "@"),
+  ARGPARSE_s_s (oAssertPubkeyAlgo,"assert-pubkey-algo", "@"),
 
   ARGPARSE_header ("Input", N_("Options controlling the input")),
 
@@ -1044,9 +1046,12 @@ static struct compatibility_flags_s compatibility_flags [] =
 
 /* Can be set to true to force gpg to return with EXIT_FAILURE.  */
 int g10_errors_seen = 0;
-/* If opt.assert_signer_list is used and this variabale is not true
+/* If opt.assert_signer_list is used and this variable is not true
  * gpg will be forced to return EXIT_FAILURE.  */
 int assert_signer_true = 0;
+/* If opt.assert_pubkey_algo is used and this variable is not true
+ * gpg will be forced to return EXIT_FAILURE.  */
+int assert_pubkey_algo_false = 0;
 
 
 static int utf8_strings =
@@ -3770,6 +3775,18 @@ main (int argc, char **argv)
             add_to_strlist (&opt.assert_signer_list, pargs.r.ret_str);
 	    break;
 
+          case oAssertPubkeyAlgo:
+            if (!opt.assert_pubkey_algos)
+              opt.assert_pubkey_algos = xstrdup (pargs.r.ret_str);
+            else
+              {
+                char *tmp = opt.assert_pubkey_algos;
+                opt.assert_pubkey_algos = xstrconcat (tmp, ",",
+                                                      pargs.r.ret_str, NULL);
+                xfree (tmp);
+              }
+	    break;
+
           case oKbxBufferSize:
             keybox_set_buffersize (pargs.r.ret_ulong, 0);
             break;
@@ -5472,6 +5489,17 @@ emergency_cleanup (void)
 void
 g10_exit( int rc )
 {
+  if (rc)
+    ;
+  else if (log_get_errorcount(0))
+    rc = 2;
+  else if (g10_errors_seen)
+    rc = 1;
+  else if (opt.assert_signer_list && !assert_signer_true)
+    rc = 1;
+  else if (opt.assert_pubkey_algos && assert_pubkey_algo_false)
+    rc = 1;
+
   /* If we had an error but not printed an error message, do it now.
    * Note that write_status_failure will never print a second failure
    * status line. */
@@ -5496,15 +5524,6 @@ g10_exit( int rc )
   gnupg_block_all_signals ();
   emergency_cleanup ();
 
-  if (rc)
-    ;
-  else if (log_get_errorcount(0))
-    rc = 2;
-  else if (g10_errors_seen)
-    rc = 1;
-  else if (opt.assert_signer_list && !assert_signer_true)
-    rc = 1;
-
   exit (rc);
 }
 
diff --git a/g10/gpgv.c b/g10/gpgv.c
index f2895563e..c3b09f752 100644
--- a/g10/gpgv.c
+++ b/g10/gpgv.c
@@ -68,6 +68,7 @@ enum cmd_and_opt_values {
   oWeakDigest,
   oEnableSpecialFilenames,
   oDebug,
+  oAssertPubkeyAlgo,
   aTest
 };
 
@@ -91,6 +92,7 @@ static gpgrt_opt_t opts[] = {
                 N_("|ALGO|reject signatures made with ALGO")),
   ARGPARSE_s_n (oEnableSpecialFilenames, "enable-special-filenames", "@"),
   ARGPARSE_s_s (oDebug, "debug", "@"),
+  ARGPARSE_s_s (oAssertPubkeyAlgo,"assert-pubkey-algo", "@"),
 
   ARGPARSE_end ()
 };
@@ -119,6 +121,7 @@ static struct debug_flags_s debug_flags [] =
 
 int g10_errors_seen = 0;
 int assert_signer_true = 0;
+int assert_pubkey_algo_false = 0;
 
 static char *
 make_libversion (const char *libname, const char *(*getfnc)(const char*))
@@ -251,6 +254,19 @@ main( int argc, char **argv )
         case oEnableSpecialFilenames:
           enable_special_filenames ();
           break;
+
+        case oAssertPubkeyAlgo:
+          if (!opt.assert_pubkey_algos)
+            opt.assert_pubkey_algos = xstrdup (pargs.r.ret_str);
+          else
+            {
+              char *tmp = opt.assert_pubkey_algos;
+              opt.assert_pubkey_algos = xstrconcat (tmp, ",",
+                                                    pargs.r.ret_str, NULL);
+              xfree (tmp);
+            }
+          break;
+
         default : pargs.err = ARGPARSE_PRINT_ERROR; break;
 	}
     }
@@ -288,10 +304,18 @@ main( int argc, char **argv )
 
 
 void
-g10_exit( int rc )
-{
-  rc = rc? rc : log_get_errorcount(0)? 2 : g10_errors_seen? 1 : 0;
-  exit(rc );
+g10_exit (int rc)
+{
+  if (rc)
+    ;
+  else if (log_get_errorcount(0))
+    rc = 2;
+  else if (g10_errors_seen)
+    rc = 1;
+  else if (opt.assert_pubkey_algos && assert_pubkey_algo_false)
+    rc = 1;
+
+  exit (rc);
 }
 
 
diff --git a/g10/keydb.h b/g10/keydb.h
index b18f6e93a..798c24da3 100644
--- a/g10/keydb.h
+++ b/g10/keydb.h
@@ -487,6 +487,7 @@ const char *key_origin_string (int origin);
 /*-- keyid.c --*/
 int pubkey_letter( int algo );
 char *pubkey_string (PKT_public_key *pk, char *buffer, size_t bufsize);
+int compare_pubkey_string (const char *astr, const char *bstr);
 #define PUBKEY_STRING_SIZE 32
 u32 v3_keyid (gcry_mpi_t a, u32 *ki);
 void hash_public_key( gcry_md_hd_t md, PKT_public_key *pk );
diff --git a/g10/keyid.c b/g10/keyid.c
index 89bba0d7a..ce977de0b 100644
--- a/g10/keyid.c
+++ b/g10/keyid.c
@@ -140,6 +140,130 @@ pubkey_string (PKT_public_key *pk, char *buffer, size_t bufsize)
 }
 
 
+/* Helper for compare_pubkey_string.  This skips leading spaces,
+ * commas and optional condition operators and returns a pointer to
+ * the first non-space character or NULL in case of an error.  The
+ * length of a prefix consisting of letters is then returned ar PFXLEN
+ * and the value of the number (e.g. 384 for "brainpoolP384r1") at
+ * NUMBER.  R_LENGTH receives the entire length of the algorithm name
+ * which is terminated by a space, nul, or a comma.  If R_CONDITION is
+ * not NULL, 0 is stored for a leading "=", 1 for a ">", 2 for a ">=",
+ * -1 for a "<", and -2 for a "<=".  If R_CONDITION is NULL no
+ * condition prefix is allowed.  */
+static const char *
+parse_one_algo_string (const char *str, size_t *pfxlen, unsigned int *number,
+                       size_t *r_length, int *r_condition)
+{
+  int condition = 0;
+  const char *result;
+
+  while (spacep (str) || *str ==',')
+    str++;
+  if (!r_condition)
+    ;
+  else if (*str == '>' && str[1] == '=')
+    condition = 2, str += 2;
+  else if (*str == '>' )
+    condition = 1, str += 1;
+  else if (*str == '<' && str[1] == '=')
+    condition = -2, str += 2;
+  else if (*str == '<')
+    condition = -1, str += 1;
+  else if (*str == '=')  /* Default.  */
+    str += 1;
+
+  if (!alphap (str))
+    return NULL;  /* Error.  */
+
+  *pfxlen = 1;
+  for (result = str++; alphap (str); str++)
+    ++*pfxlen;
+  while (*str == '-' || *str == '+')
+    str++;
+  *number = atoi (str);
+  while (*str && !spacep (str) && *str != ',')
+    str++;
+
+  *r_length = str - result;
+  if (r_condition)
+    *r_condition = condition;
+  return result;
+}
+
+/* Helper for compare_pubkey_string.  If BPARSED is set to 0 on
+ * return, an error in ASTR or BSTR was found and further checks are
+ * not possible.  */
+static int
+compare_pubkey_string_part (const char *astr, const char *bstr_arg,
+                            size_t *bparsed)
+{
+  const char *bstr = bstr_arg;
+  size_t alen, apfxlen, blen, bpfxlen;
+  unsigned int anumber, bnumber;
+  int condition;
+
+  *bparsed = 0;
+  astr = parse_one_algo_string (astr, &apfxlen, &anumber, &alen, &condition);
+  if (!astr)
+    return 0;  /* Invalid algorithm name.  */
+  bstr = parse_one_algo_string (bstr, &bpfxlen, &bnumber, &blen, &condition);
+  if (!bstr)
+    return 0;  /* Invalid algorithm name.  */
+  *bparsed = blen + (bstr - bstr_arg);
+  if (apfxlen != bpfxlen || ascii_strncasecmp (astr, bstr, apfxlen))
+    return 0;  /* false.  */
+  switch (condition)
+    {
+    case 2: return anumber >= bnumber;
+    case 1: return anumber > bnumber;
+    case -1: return anumber < bnumber;
+    case -2: return anumber <= bnumber;
+    }
+
+  return alen == blen && !ascii_strncasecmp (astr, bstr, alen);
+}
+
+
+/* Check whether ASTR matches the constraints given by BSTR.  ASTR may
+ * be any algo string like "rsa2048", "ed25519" and BSTR may be a
+ * constraint which is in the simplest case just another algo string.
+ * BSTR may have more that one string in which case they are comma
+ * separated and any match will return true.  It is possible to prefix
+ * BSTR with ">", ">=", "<=", or "<".  That prefix operator is applied
+ * to the number part of the algorithm, i.e. the first sequence of
+ * digits found before end-of-string or a comma.  Examples:
+ *
+ * | ASTR     | BSTR                 | result |
+ * |----------+----------------------+--------|
+ * | rsa2048  | rsa2048              | true   |
+ * | rsa2048  | >=rsa2048            | true   |
+ * | rsa2048  | >rsa2048             | false  |
+ * | ed25519  | >rsa1024             | false  |
+ * | ed25519  | ed25519              | true   |
+ * | nistp384 | >nistp256            | true   |
+ * | nistp521 | >=rsa3072, >nistp384 | true   |
+ */
+int
+compare_pubkey_string (const char *astr, const char *bstr)
+{
+  size_t bparsed;
+  int result;
+
+  while (*bstr)
+    {
+      result = compare_pubkey_string_part (astr, bstr, &bparsed);
+      if (result)
+        return 1;
+      if (!bparsed)
+        return 0; /* Syntax error in ASTR or BSTR.  */
+      bstr += bparsed;
+    }
+
+  return 0;
+}
+
+
+
 /* Hash a public key and allow to specify the to be used format.
  * Note that if the v5 format is requested for a v4 key, a 0x04 as
  * version is hashed instead of the 0x05. */
diff --git a/g10/main.h b/g10/main.h
index b29e23e51..2482fbde2 100644
--- a/g10/main.h
+++ b/g10/main.h
@@ -84,6 +84,7 @@ struct weakhash
 /*-- gpg.c --*/
 extern int g10_errors_seen;
 extern int assert_signer_true;
+extern int assert_pubkey_algo_false;
 
 #if __GNUC__ > 2 || (__GNUC__ == 2 && __GNUC_MINOR__ >= 5 )
   void g10_exit(int rc) __attribute__ ((__noreturn__));
@@ -494,6 +495,7 @@ int verify_signatures (ctrl_t ctrl, int nfiles, char **files );
 int verify_files (ctrl_t ctrl, int nfiles, char **files );
 int gpg_verify (ctrl_t ctrl, int sig_fd, int data_fd, estream_t out_fp);
 void check_assert_signer_list (const char *mainpkhex, const char *pkhex);
+void check_assert_pubkey_algo (const char *algostr, const char *pkhex);
 
 /*-- decrypt.c --*/
 int decrypt_message (ctrl_t ctrl, const char *filename );
diff --git a/g10/mainproc.c b/g10/mainproc.c
index 430d7ff08..5f3f6df86 100644
--- a/g10/mainproc.c
+++ b/g10/mainproc.c
@@ -1876,6 +1876,8 @@ check_sig_and_print (CTX c, kbnode_t node)
   const void *extrahash = NULL;
   size_t extrahashlen = 0;
   kbnode_t included_keyblock = NULL;
+  char pkstrbuf[PUBKEY_STRING_SIZE] = { 0 };
+
 
   if (opt.skip_verify)
     {
@@ -2409,8 +2411,14 @@ check_sig_and_print (CTX c, kbnode_t node)
             show_notation (sig, 0, 2, 0);
         }
 
+      /* Fill PKSTRBUF with the algostring in case we later need it.  */
+      if (pk)
+        pubkey_string (pk, pkstrbuf, sizeof pkstrbuf);
+
       /* For good signatures print the VALIDSIG status line.  */
-      if (!rc && (is_status_enabled () || opt.assert_signer_list) && pk)
+      if (!rc && (is_status_enabled ()
+                  || opt.assert_signer_list
+                  || opt.assert_pubkey_algos) && pk)
         {
           char pkhex[MAX_FINGERPRINT_LEN*2+1];
           char mainpkhex[MAX_FINGERPRINT_LEN*2+1];
@@ -2432,6 +2440,8 @@ check_sig_and_print (CTX c, kbnode_t node)
                                mainpkhex);
           /* Handle the --assert-signer option.  */
           check_assert_signer_list (mainpkhex, pkhex);
+          /* Handle the --assert-pubkey-algo option.  */
+          check_assert_pubkey_algo (pkstrbuf, pkhex);
 	}
 
       /* Print compliance warning for Good signatures.  */
@@ -2464,13 +2474,6 @@ check_sig_and_print (CTX c, kbnode_t node)
 
       if (opt.verbose)
         {
-          char pkstrbuf[PUBKEY_STRING_SIZE];
-
-          if (pk)
-            pubkey_string (pk, pkstrbuf, sizeof pkstrbuf);
-          else
-            *pkstrbuf = 0;
-
           log_info (_("%s signature, digest algorithm %s%s%s\n"),
                     sig->sig_class==0x00?_("binary"):
                     sig->sig_class==0x01?_("textmode"):_("unknown"),
diff --git a/g10/options.h b/g10/options.h
index 146b78361..1e1110334 100644
--- a/g10/options.h
+++ b/g10/options.h
@@ -241,6 +241,10 @@ struct
    * modify to be uppercase if they represent a fingerrint */
   strlist_t assert_signer_list;
 
+  /* A single string with the comma delimited args from
+   * --assert-pubkey_algo.  */
+  char *assert_pubkey_algos;
+
   struct
   {
     /* If set, require an 0x19 backsig to be present on signatures
diff --git a/g10/t-keydb-get-keyblock.c b/g10/t-keydb-get-keyblock.c
index e40be9cc1..90ce6e9a6 100644
--- a/g10/t-keydb-get-keyblock.c
+++ b/g10/t-keydb-get-keyblock.c
@@ -67,12 +67,3 @@ do_test (int argc, char *argv[])
   release_kbnode (kb1);
   xfree (ctrl);
 }
-
-int assert_signer_true = 0;
-
-void
-check_assert_signer_list (const char *mainpkhex, const char *pkhex)
-{
-  (void)mainpkhex;
-  (void)pkhex;
-}
diff --git a/g10/t-keydb.c b/g10/t-keydb.c
index 9055d5b94..4c78dac48 100644
--- a/g10/t-keydb.c
+++ b/g10/t-keydb.c
@@ -105,13 +105,3 @@ do_test (int argc, char *argv[])
   keydb_release (hd2);
   xfree (ctrl);
 }
-
-
-int assert_signer_true = 0;
-
-void
-check_assert_signer_list (const char *mainpkhex, const char *pkhex)
-{
-  (void)mainpkhex;
-  (void)pkhex;
-}
diff --git a/g10/t-keyid.c b/g10/t-keyid.c
new file mode 100644
index 000000000..d42399027
--- /dev/null
+++ b/g10/t-keyid.c
@@ -0,0 +1,129 @@
+/* t-keyid.c - Tests for keyid.c.
+ * Copyright (C) 2024 g10 Code GmbH
+ *
+ * This file is part of GnuPG.
+ *
+ * GnuPG is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * GnuPG is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <https://www.gnu.org/licenses/>.
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
+#include <config.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#define LEAN_T_SUPPORT 1
+
+#define PGM "t-keyid"
+
+#include "gpg.h"
+#include "keydb.h"
+#include "../common/t-support.h"
+
+
+
+static int verbose;
+
+
+static void
+test_compare_pubkey_string (void)
+{
+  static struct { const char *astr; const char *bstr; int expected; } t[] =
+  {
+    { "rsa2048"  , "rsa2048"             ,  1 },
+    { "rsa2048"  , ">=rsa2048"           ,  1 },
+    { "rsa2048"  , ">rsa2048"            ,  0 },
+    { "ed25519"  , ">rsa1024"            ,  0 },
+    { "ed25519"  , "ed25519"             ,  1 },
+    { "ed25519"  , ",,,=ed25519"         ,  1 },
+    { "nistp384" , ">nistp256"           ,  1 },
+    { "nistp521" , ">=rsa3072, >nistp384",  1 },
+    { " nistp521" , ">=rsa3072, >nistp384   ",  1 },
+    { "  nistp521  " , "  >=rsa3072, >nistp384   ",  1 },
+    { "  =nistp521  " , "  >=rsa3072, >nistp384,,",  1 },
+    { "nistp384" , ">nistp384"           ,  0 },
+    { "nistp384" , ">=nistp384"          ,  1 },
+    { "brainpoolP384" , ">=brainpoolp256", 1 },
+    { "brainpoolP384" , ">brainpoolp384" , 0 },
+    { "brainpoolP384" , ">=brainpoolp384", 1 },
+    { "brainpoolP256r1", ">brainpoolp256r1", 0 },
+    { "brainpoolP384r1", ">brainpoolp384r1" , 0 },
+    { "brainpoolP384r1", ">=brainpoolp384r1", 1 },
+    { "brainpoolP384r1", ">=brainpoolp384"  , 1 },
+    { "",  "", 0}
+  };
+  int idx;
+  int result;
+
+  for (idx=0; idx < DIM(t); idx++)
+    {
+      result = compare_pubkey_string (t[idx].astr, t[idx].bstr);
+      if (result != t[idx].expected)
+        {
+          fail (idx);
+          if (verbose)
+            log_debug ("\"%s\", \"%s\" want %d got %d\n",
+                       t[idx].astr, t[idx].bstr, t[idx].expected, result);
+        }
+    }
+
+}
+
+
+int
+main (int argc, char **argv)
+{
+  int last_argc = -1;
+
+  no_exit_on_fail = 1;
+
+  if (argc)
+    { argc--; argv++; }
+  while (argc && last_argc != argc )
+    {
+      last_argc = argc;
+      if (!strcmp (*argv, "--"))
+        {
+          argc--; argv++;
+          break;
+        }
+      else if (!strcmp (*argv, "--help"))
+        {
+          fputs ("usage: " PGM " [FILE]\n"
+                 "Options:\n"
+                 "  --verbose         Print timings etc.\n"
+                 "  --debug           Flyswatter\n"
+                 , stdout);
+          exit (0);
+        }
+      else if (!strcmp (*argv, "--verbose"))
+        {
+          verbose++;
+          argc--; argv++;
+        }
+      else if (!strcmp (*argv, "--debug"))
+        {
+          verbose += 2;
+          argc--; argv++;
+        }
+      else if (!strncmp (*argv, "--", 2))
+        {
+          fprintf (stderr, PGM ": unknown option '%s'\n", *argv);
+          exit (1);
+        }
+    }
+
+  test_compare_pubkey_string ();
+
+  return !!errcount;
+}
diff --git a/g10/t-stutter.c b/g10/t-stutter.c
index 7b2ea4b37..503a92004 100644
--- a/g10/t-stutter.c
+++ b/g10/t-stutter.c
@@ -611,12 +611,3 @@ do_test (int argc, char *argv[])
 
   xfree (filename);
 }
-
-int assert_signer_true = 0;
-
-void
-check_assert_signer_list (const char *mainpkhex, const char *pkhex)
-{
-  (void)mainpkhex;
-  (void)pkhex;
-}
diff --git a/g10/test-stubs.c b/g10/test-stubs.c
index 6ae0f4eb7..d9bead754 100644
--- a/g10/test-stubs.c
+++ b/g10/test-stubs.c
@@ -43,6 +43,9 @@
 #include "call-agent.h"
 
 int g10_errors_seen;
+int assert_signer_true = 0;
+int assert_pubkey_algo_false = 0;
+
 
 
 void
@@ -580,3 +583,18 @@ impex_filter_getval (void *cookie, const char *propname)
   (void)propname;
   return NULL;
 }
+
+
+void
+check_assert_signer_list (const char *mainpkhex, const char *pkhex)
+{
+  (void)mainpkhex;
+  (void)pkhex;
+}
+
+void
+check_assert_pubkey_algo (const char *algostr, const char *pkhex)
+{
+  (void)algostr;
+  (void)pkhex;
+}
diff --git a/g10/test.c b/g10/test.c
index 648148a10..f6c697a35 100644
--- a/g10/test.c
+++ b/g10/test.c
@@ -15,6 +15,7 @@
  *
  * You should have received a copy of the GNU General Public License
  * along with this program; if not, see <https://www.gnu.org/licenses/>.
+ * SPDX-License-Identifier: GPL-3.0-or-later
  */
 
 #include <config.h>
diff --git a/g10/verify.c b/g10/verify.c
index e9792939d..1c3de767c 100644
--- a/g10/verify.c
+++ b/g10/verify.c
@@ -333,7 +333,7 @@ check_assert_signer_list (const char *mainpkhex, const char *pkhex)
               assert_signer_true = 1;
               write_status_text (STATUS_ASSERT_SIGNER, item->d);
               if (!opt.quiet)
-                log_info ("signer '%s' matched\n", item->d);
+                log_info ("asserted signer '%s'\n", item->d);
               goto leave;
             }
         }
@@ -388,7 +388,7 @@ check_assert_signer_list (const char *mainpkhex, const char *pkhex)
                   assert_signer_true = 1;
                   write_status_text (STATUS_ASSERT_SIGNER, p);
                   if (!opt.quiet)
-                    log_info ("signer '%s' matched '%s', line %d\n",
+                    log_info ("asserted signer '%s' (%s:%d)\n",
                               p, fname, lnr);
                   goto leave;
                 }
@@ -405,3 +405,32 @@ check_assert_signer_list (const char *mainpkhex, const char *pkhex)
  leave:
   es_fclose (fp);
 }
+
+
+/* This function shall be called with the signer's public key
+ * algorithm ALGOSTR iff a signature is fully valid.  If the option
+ * --assert-pubkey-algo is active the functions checks whether the
+ * signing key's algo is valid according to that list; in this case a
+ * global flag is set.  */
+void
+check_assert_pubkey_algo (const char *algostr, const char *pkhex)
+{
+  if (!opt.assert_pubkey_algos)
+    return;  /* Nothing to do.  */
+
+  if (compare_pubkey_string (algostr, opt.assert_pubkey_algos))
+    {
+      write_status_strings (STATUS_ASSERT_PUBKEY_ALGO,
+                            pkhex, " 1 ", algostr, NULL);
+      if (!opt.quiet)
+        log_info ("asserted signer '%s' with algo %s\n", pkhex, algostr);
+    }
+  else
+    {
+      if (!opt.quiet)
+        log_info ("denied signer '%s' with algo %s\n", pkhex, algostr);
+      assert_pubkey_algo_false = 1;
+      write_status_strings (STATUS_ASSERT_PUBKEY_ALGO,
+                            pkhex, " 0 ", algostr, NULL);
+    }
+}